Getting tougher on drugs has been the mantra of political hacks on both the left and right for 40 years. If they can't solve any real issues, they always had the drug war to fall back on. Now the public is waking up to the fact that the drug war in general and marijuana prohibition in particular is based on lies, exaggeration and junk science. Legislators will figure out very quickly that standing with the prohibitionists is going to cost them elections.

Increasingly, the law is an excuse for pigs to bully people. It's no longer about protecting people; a pig today is in a career environment where the goal is to make arrests, and they brutalize people as necessary to accomplish that.

You have a point, but within the scope of what is illegal the police have a choice generally as to what they make a priority. Jaywalking is also against the law. Throwing resources into marijuana sting operations and buy/bust arrests is choosing to prioritize this over other crime, because man hours and budgets are a zero sum game.

While strictly true, it's also not the whole point. Most laws on the books are almost never enforced, and even then only selectively. For example, violating the terms of service of any software, website, or ISP you use is technically a felony according to some U.S. courts http://boingboing.net/2013/01/16/aarons-law-introduced-w.htmlMoreover, in polls somewhere between a quarter and a half of U.S. adults have used pot - what do you think the unemployment and incarceration rates would be if drug laws were actually enforced?

So, the police already have wide discretion. It's a necessity, because the people who write the laws seem to have little interest in writing better ones. The only real question is how the police use that discretion, where they put their (again, of necessity) limited funding.